The genus Coffea consists of about 70 species of which C. arabica is the most economically important. This species accounts for about 70% of the estimated $15 billion annual market. Although other species of Coffea have such potentially desirable genetic traits as, for example, the absence of caffeine production and disease resistance, these species are generally undesirable because of other factors such as low yield of beans or beans which produce a poor quality coffee. While it would be desirable to combine these genetic traits with those of C. arabica, traditional plant breeding techniques have been largely unsuccessful since C. arabica is tetraploid whereas the other species are diploid. The non-arabica species are also self-incompatible. As a result, the transfer of genetic traits from wild outbred species of the genus to the cultivated C. arabica cultivar is quite difficult. A further complication is Coffea's lengthy period for fruit development and the 2-4 year bean-to-bean generation time which make such traditional approaches costly and time consuming.
More recently, interest has turned to in vitro cell culture and recombinant techniques in order to genetically modify members of the genus Coffea. In vitro techniques have been applied to various aspects in the cultivation of coffee. Staritsky (Acta Bot. Neerl., 19:509, 1970 ) induced callus tissues from orthotropic shoots of C. canephora, C. arabica and C. liberica, but obtained somatic embryos and plantlets only from C. canephora. Callus from endosperm tissues of C. arabica was induced by Keller, et al. (Planta, 108:339, 1972) for the purpose of studying caffeine synthesis. Sharp, et al. (Phyton, 31:67, 1973) cultured somatic and haploid tissues of C. arabica and obtained callus growth (petioles, leaves, green fruits), proembryo formation (anthers) and shoot development (orthotropic shoots). For the purpose of producing coffee aroma from suspension cultures, Townsley (Can. Inst. Food Sci. Technol., 7:79, 1974) established liquid cultures of coffee cells from friable callus derived from orthotropic shoots of C. arabica. The distinction of high and low frequencies of somatic embryo induction from cultured mature leaf explants of C. arabica (cultivar Bourbon) were described by Sondahl, et al. (Abstract, International Conference on Regulation of Developmental Processes in Plants, Halle, 180, 1977). In addition, protoplasts have been isolated from leaf-derived callus tissues of C. arabica (cultivar Bourbon) and callus regeneration was obtained in about 30% of the cultures (Staritsky, Acta Bot. Neerl., 19:509, 1970). However, no plant regeneration from these calli were reported. More recently, Schopke, et al., ( Plant Cell, Tissue and Organ Culture, 8:243, 1987) reported the somatic embryogenesis and regeneration of plantlets in protoplast cultures from somatic embryos of C. canephora.
Although considerable research has been done to asexually modify the genetic composition of the various species of Coffea, to date attempts to regenerate stable genetically modified whole plants from protoplasts have been unsuccessful. Thus, there is considerable need for plants of the genus Coffea which are genetically modified and stable such that the genetic modification is transmitted to progeny.